1. Field of the Invention
The present invention relates to a battery pack for use with a video camera and a battery charger for charging the battery pack.
2. Description of the Prior Art
For outdoor use of a video camera, for example, a battery pack is usually mounted on the video camera as a portable electric power supply that makes the video camera handy in areas where no commercial electric power outlets are available.
FIG. 1 of the accompanying drawings shows one conventional battery pack for use on a video camera. As shown in FIG. 1, the battery pack comprises a cell array 7 composed of juxtaposed cylindrical nickel-cadmium secondary cells 1, 2, 3, 4, 5 that are electrically connected by a conductor plate 6 and other conductors. An electrically insulating sheet 8 is inserted between the conductor plate 6 and the cells 2, 3, 4. The cell array 7 has first and second electrodes 9, 10 as positive and negative electrodes for charging and discharging the battery pack. A breaker (not shown) is held by a molded member 11 below the first and second electrodes 9, 10. The cell array 7 and the other components are housed in a plastic casing 14 which comprises upper and lower casing members 12, 13. The casing 14 is substantially in the shape of a rectangular parallelepiped such that it houses the cell array 7 in intimate contact therewith for reducing the size and weight of the battery pack.
To charge the battery pack, it is generally mounted on a dedicated battery charger (not shown). For proper mounting of the battery pack on the battery charger, the lower case 13 that will contact the battery charger has a plurality of integral recesses 16, and the battery charger has a plurality of teeth on its case for engagement in the respective recesses 16 in the lower case 13. The recesses 16 are positioned in gaps 17A.about.17D, respectively, between the cells 1.about.5 for the reduction of the size and weight of the battery pack.
There are demands for video camera battery packs of small size and large energy storage capacity.
When battery packs of nickel-hydrogen secondary cells are quickly charged, their temperature rises more sharply than the temperature of battery packs of nickel-cadmium secondary cells. Therefore, the charging process for a nickel-hydrogen battery pack has to be controlled while monitoring the temperature thereof. For such charging process control, it is necessary for the battery pack to have a temperature detecting element such as a thermistor or the like, and a third electrode for outputting a detected signal from the temperature detecting element, and also for a battery charger to have a third terminal for receiving the detected signal from the third electrode, and a control circuit for controlling the charging process based on the received signal. Such a battery charger should preferably be compatible for use with different types of battery packs so that it can also be used to charge conventional battery packs of the type shown in FIG. 1 that are widely available on the market.
One problem with the prior battery pack shown in FIG. 1 is that since the cell array 7 and other components are already closely positioned in the casing 14, it is not easy to create a space large enough to accommodate the third electrode. Furthermore, the third electrode must be incorporated in a layout that is designed taking account of safety and reliability considerations.